1. Field of the Invention
The present invention relates to parking assistance apparatus for assisting parking by picking up the rear direction of a vehicle by using a vehicle-mounted camera and displaying the resulting image on a screen that can be viewed from the driver's seat, and in particular to parking assistance apparatus for assisting parking by superimposing a guide on the screen.
2. Description of the Related Art
Driving assistance apparatus has been in widespread use that provides the driver of the view at the rear direction of a vehicle without the driving looking into a rearview mirror, by mounting a vehicle-mounted camera on the rear trunk of a vehicle in a rear direction and presenting the image obtained from the vehicle-mounted camera to the driver. In particular, in recent years, driving assistance apparatus has been on the market (for example, Japanese Patent Laid-Open Hei 11-337740) that superimposes the predicted locus of the tires of a vehicle corresponding to the steering angle on the image shot by the camera and presented to the driver in order to notify the predicted direction of the vehicle.
However, driving assistance apparatus that superimposes the predicted travel locus moving with the variation in the steering angle on the image shot by a vehicle-mounted camera has outstanding problems.
A first problem is that a steering angle sensor is expensive and a processing unit to compute the predicted locus of the travel direction of the tires by using sensor information from the steering angle sensor is also required thus increasing the price of the vehicle. A second problem is that errors in the predicted locus are accumulated as the steering angle sensor is used for longer time thus causing a displacement from the actual locus. Another problem is that an unskilled driver cannot easily determine the parking start position or timing to turn back the wheel when he/she has checked the predicted locus moving with the variation in the steering angle of the wheel. The driver needs some practice before he/she has accustomed to the system.
Thus, as driving assistance apparatus that allows easy parking without using a steering angle sensor is provided for example in the Japanese Patent Laid-Open Hei 12-078566 or Japanese Patent Laid-Open 2000-168475.
To perform end-to-end parking or side-by-side parking of a vehicle including parking of a vehicle in a garage, parking is often accomplished by backing the vehicle with wheel position fixed (for example steering to left) once the start position of parking is found. A related art technology described in the Japanese Patent Laid-Open Hei 12-078566 focuses on this fact and discloses a technology that superimposes on the image picked up by a vehicle-mounted camera the vehicle space at the destination the vehicle is expected to reach in case the vehicle is backed with the wheel turned at the maximum steering angle.
A related art technology described in the Japanese Patent Laid-Open 2000-168475 guides the parking procedure by displaying the predicted vehicle travel locus assumed when the wheel is steered. This is based on the idea that the driver has only to steer the wheel to back the vehicle once he/she has guided the vehicle so that the destination of the predicted locus will reach the parking space. This philosophy is basically the same as the related art in the Japanese Patent Laid-Open Hei 12-78566.
FIG. 37 is a schematic view of a screen display example of related art driving assistance apparatus. In FIG. 37, a rear end 1a of the vehicle and a rectangular area guide 1b showing as a guide the approximate size of the vehicle space are displayed. Assume a case where the vehicle 1 is parked into parking space 4 before another vehicle 2 that is parked, as shown in FIG. 38A. In this case, the driver watches the screen display shown in FIG. 38B and moves the vehicle 1 so that the position of the area guide 1b described referring to FIG. 37 will match the space adjacent to an image 2a of another vehicle 2. Then, backing the vehicle with the wheel fully turned to the left brings the vehicle 1 into the space of the area guide 1b. The driver has only to position the vehicle at the start of parking procedure so that the position of the area guide on the screen matches the target location, then back the vehicle with the wheel steered.
Related art driving assistance apparatus in FIGS. 38A and 38B still has problems that the alignment of the vehicle at completion of parking is difficult and that the vehicle could come in contact with another vehicle.
Related art apparatus described in the Japanese Patent Laid-Open Hei 12-078566/2000 assumes parking by backing a vehicle until the vehicle turns 90 degrees with the steering angle set to the maximum. Thus, the parking space shown in the area guide is too far from the parking start position so that the parking space (area guide) in the screen is very small thus making it difficult to align the vehicle at the end of parking. That is, the position of the vehicle at the end of parking is often too close to or too far from the adjacent vehicle.
The method to change the direction of a vehicle 90 degrees at once differs from the vehicle guidance method of side-by-side parking conventionally used by many drivers, which perplexes the driver. As shown in FIG. 39, the related art vehicle guidance method of side-by-side parking comprises: the step of driving the vehicle 1 to bring the vehicle close to the parking space 4 with the vehicle at perpendicular to the parking space 4 (step P1); the step of directing the rear of the vehicle toward the parking space 4 by advancing the vehicle with the wheel turned in the direction opposite to the parking space (step P2); turning back the wheel and backing the vehicle to place the vehicle in the center of the parking space 4 parallel to other vehicles (step P3); and backing the vehicle with the wheel held straight to place the vehicle in the parking space 4 (step P4). It is a problem to oblige the driver to follow a parking method other than this approach. Rather, it is preferable to diffuse driving assistance apparatus to assist the related art vehicle guidance method for side-by-side parking.
In related art apparatus described in the Japanese Patent Laid-Open 2000-168475, only the predicted travel locus assumed when the wheel is in straight position and when the wheel is steered. In case the parking space is split by a parking border line painted on the road surface, it is possible to back the vehicle using the parking border line as a guide. In the absence of a parking border line, the driver must use the predicted travel locus on the screen as a guide to back the vehicle. In such a case, the vehicle has a higher possibility to come in contact with an adjacent vehicle. This will be explained referring to FIGS. 40A and 40B.
FIG. 40A shows the state of the step P3 for side-by-side parking. A parking border line shown by a numeral 5 in FIG. 39 is not displayed on the road surface. FIG. 40B shows the image shot by a vehicle-mounted camera on the screen, where the predicted travel locus of the vehicle is superimposed. FIG. 40B shows that the predicted travel locus shows that the predicted travel locus 6 while the wheel is steered grazes a point between the front tire and the rear tire of the image of the vehicle parked in the parking space. As seen from this image, the predicted travel locus 6 does not overlap the adjacent vehicle image 2. So, it seems that backing the vehicle as indicated does not bring the vehicle in contact with the adjacent vehicle 2.
However, checking the detailed situation, the predicted travel locus 6 crosses the straight line LT connecting the ground points of the front and rear tires of the vehicle image 2a. It is sure that backing the vehicle in this direction brings the vehicle 1 into contact with the adjacent vehicle 2. As such, using the predicted travel locus alone makes it difficult to determine the contact of the vehicle with surrounding vehicles.